The fuel consumption of automotive engines may be improved by shutting off fuel delivery into an engine when a vehicle is decelerating. This is known as deceleration fuel shut-off (DFSO). However, during DFSO the delivery of oxygen into an emissions control device of the vehicle increases. In vehicles that include a particulate filter, this increased oxygen delivery may result in degradation of the filter due to the overheating of the filter.
U.S. Pat. No. 8,407,988 offers a method to reduce the flow of oxygen to the particle filter during non-combustion conditions by closing an intake throttle valve. However, the inventors herein have recognized an issue with the above approach. As the engine continues to rotate with the intake throttle valve closed, the intake manifold air pressure (MAP) begins to drop. If the MAP gets too low, engine degradation may occur, e.g., lubricants may be drawn into the combustion chamber.
Accordingly, the inventors herein provide an approach to at least partially address these issues. In one example, a method includes, in response to a determination that a particle filter has reached a temperature above a threshold while an engine is operating with deceleration fuel shut-off (DFSO), fully closing a throttle valve configured to regulate flow of intake air to the engine, and responsive to intake manifold pressure dropping below a threshold pressure while the throttle valve is fully closed, adjusting a position of the throttle valve based on the particulate filter temperature.
In this way, particulate filter temperature during DFSO may be maintained below a threshold temperature, thus preventing filter degradation and extending the length of operation of DFSO. If the MAP drops below a threshold pressure while the throttle valve is closed, the throttle valve position may be adjusted based on filter temperature. For example, if the filter temperature is above the threshold temperature yet below an upper limit threshold, the throttle valve may be open by a small, preset amount. However, if the temperature of the particle filter increases above the upper limit threshold to the throttle may be maintained fully closed and MAP may be controlled by adjusting intake and/or exhaust valve timing to increase the overlap between the intake and exhaust valves of an engine's cylinders in order to increase the manifold pressure. In doing so, the MAP may be increased while maintaining restricted airflow into the particle filter, and in this way help decrease the temperature of the particle filter, while the engine remains in DFSO mode.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.